It is known that the perceived slant of an inclined surface produced by horizontal disparity decreases due to adaptation after it is viewed for a certain time. The effect of gaze direction on adaptation to a stereo-slant was investigated. A random dot stereogram (RDS) rotated around a vertical axis, viewed at a distance of 57 cm was used as both the adaptation and test stimulus. Adaptation was measured by two tests. In the first test, the RDS for measuring the slant adaptation and the fixation point were displayed straight ahead of the participant, along with an adaptation stimulus. In the second test, RDS for measurement and fixation point were displayed at a vertical shift of 4°, whereas the adaptation stimulus was continuously displayed straight ahead. In both conditions, adaptation and measurements were made on the central visual field of the retina. Results indicated that significantly less adaptation was observed in the second test compared to the first. This result suggests that stereo-slant adaptation is partially affected by gaze direction. Moreover, it also suggests that the site of stereo-slant adaptation is determined after the eye position signal is merged with information about binocular disparity.